| | 1 | Author
| HorstW. Alter | Requires cookie* | | | Title
| Permeability of Plasma Membrane Vesicles to Ouabain and Mg2+ as a Factor Determining Rate of Binding of Ouabain to Na+ and K+ Dependent ATPase  | | | | Abstract
| N a+, K+-ATPase of the plasma membrane isolated from sheep kidney medulla exhibits functio nal asymmetry for the cardiac glycoside ouabain. In this vesicular membrane preparation the rate of binding o f ouabain was slow (time constant > 60 min) when the vesicles were incubated in the presence o f isotonic sucrose. Upon treatment o f the preparation with hypoosmotic shock or phos-pholipase A the initial rate of ouabain binding was enhanced at least 3 fold. In equilibrium a concentration of the ouabain-enzyme-complex was obtained which was about twofold that of the untreated vesicles. This result suggests two types o f ouabain binding sites with an approximate stoichiometry of 1 to 1. The stoichiometry seems to be maintained at high concentrations of ouabain where binding curves show a biphasic time course. Additional information about hetero geneity of binding sites comes through experiments in which the vesicles were treated with Mg2+ prior to the addition o f ouabain. A minor fraction of the binding sites were occupied by ouabain only after longtime incubation with Mg2+. | | | |
Reference
| Z. Naturforsch. 34c, 1224 (1979); received July 13/August 18 1979 | | | |
Published
| 1979 | | | |
Keywords
| N a+, K+-ATPase, Plasma Membrane Vesicles, Cardiac Glycoside, Magnesium, Tightness | | | |
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| default:Reihe_C/34/ZNC-1979-34c-1224.pdf | | | | Identifier
| ZNC-1979-34c-1224 | | | | Volume
| 34 | |
| 2 | Author
| Maike Petersen, Ulrich Hanns, Seitz, Ernst Reinhard | Requires cookie* | | | Title
| Characterization and Localization of Digitoxin 12 ß-Hydroxylase from Cell Cultures of Digitalis lanata EHRH | | | | Abstract
| The cytochrome P-450-dependent monooxygenase digitoxin 12ß-hydroxylase from cell cultures of Digitalis lanata needs NADPH and molecular oxygen and hydroxylates cardiac glycosides with the aglycon of digitoxigenin to the corresponding derivatives of the C-series. Other electron donors cannot replace NADPH. The apparent K" m -values are 26 UM for NADPH, 7.1 ^IM for ß-methyldigitoxin and 10 ^IM for digitoxin. The reaction is inhibited by NADP + and cytochrome c in a competitive mode. The optimum temperature was at 20 °C. Low concentrations of Mn 2+ , Mg 2+ , and EDTA were slightly stimulatory, but there was no strict dependence on divalent cations. Digitoxin 12ß-hydroxylase is very stable at room temperature and the reaction proceeds for more than 20 h. After the addition of 15% glycerol, 70% of the original activity can be retained subsequent to freezing at —18 °C. By means of linear sucrose gradient fractionation of cellular membranes the digitoxin 12ß-hydroxylase was found to be located in the endoplasmic reticulum. | | | |
Reference
| Z. Naturforsch. 43c, 199—206 (1988); received December 8 1987 | | | |
Published
| 1988 | | | |
Keywords
| Cardiac Glycosides, Cytochrome P-450, Digitalis lanata, Digitoxin 12ß-Hydroxylase, Endoplas-mic Reticulum | | | |
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| default:Reihe_C/43/ZNC-1988-43c-0199.pdf | | | | Identifier
| ZNC-1988-43c-0199 | | | | Volume
| 43 | |
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